Package for an Implantable Neural Stimulation Device

ABSTRACT

An implantable device, including a first electrically non-conductive substrate; a plurality of electrically conductive vias through the first electrically non-conductive substrate; a flip-chip multiplexer circuit attached to the electrically non-conductive substrate using conductive bumps and electrically connected to at least a subset of the plurality of electrically conductive vias; a flip-chip driver circuit attached to the flip-chip multiplexer circuit using conductive bumps; a second electrically non-conductive substrate attached to the flip-chip driver circuit using conductive bumps; discrete passives attached to the second electrically non-conductive substrate; and a cover bonded to the first electrically non-conductive substrate, the cover, the first electrically non-conductive substrate and the electrically conductive vias forming a hermetic package.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of Application of U.S. patentapplication Ser. No. 13/783,225, filed Mar. 1, 2013, entitled Packagefor an Implantable Neural Stimulation Device; which is a divisionalapplication of U.S. patent application Ser. No. 11/924,709, filed Oct.26, 2007, entitled Package for an Implantable Neural Stimulation Device;which is a divisional application of U.S. patent application Ser. No.11/893,939, entitled Package for an Implantable Neural StimulationDevice, filed Aug. 18, 2007; which application claims benefit ofprovisional Application Ser. No. 60/838,714, filed on Aug. 18, 2006,entitled Package for an Implantable Neural Stimulation Device and ofprovisional Application Ser. No. 60/880,994, filed on Jan. 18, 2007,entitled Package for an Implantable Neural Stimulation Device thedisclosures of both are incorporated herein by reference.

GOVERNMENT RIGHTS NOTICE

This invention was made with government support under grant No.R24EY12893-01, awarded by the National Institutes of Health. Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

The present invention is generally directed to neural stimulation andmore specifically to an improved hermetic package for an implantableneural stimulation device.

BACKGROUND OF THE INVENTION

In 1755 LeRoy passed the discharge of a Leyden jar through the orbit ofa man who was blind from cataract and the patient saw “flames passingrapidly downwards.” Ever since, there has been a fascination withelectrically elicited visual perception. The general concept ofelectrical stimulation of retinal cells to produce these flashes oflight or phosphenes has been known for quite some time. Based on thesegeneral principles, some early attempts at devising prostheses foraiding the visually impaired have included attaching electrodes to thehead or eyelids of patients. While some of these early attempts met withsome limited success, these early prosthetic devices were large, bulkyand could not produce adequate simulated vision to truly aid thevisually impaired.

In the early 1930's, Foerster investigated the effect of electricallystimulating the exposed occipital pole of one cerebral hemisphere. Hefound that, when a point at the extreme occipital pole was stimulated,the patient perceived a small spot of light directly in front andmotionless (a phosphene). Subsequently, Brindley and Lewin (1968)thoroughly studied electrical stimulation of the human occipital(visual) cortex. By varying the stimulation parameters, theseinvestigators described in detail the location of the phosphenesproduced relative to the specific region of the occipital cortexstimulated. These experiments demonstrated: (1) the consistent shape andposition of phosphenes; (2) that increased stimulation pulse durationmade phosphenes brighter; and (3) that there was no detectableinteraction between neighboring electrodes which were as close as 2.4 mmapart.

As intraocular surgical techniques have advanced, it has become possibleto apply stimulation on small groups and even on individual retinalcells to generate focused phosphenes through devices implanted withinthe eye itself. This has sparked renewed interest in developing methodsand apparati to aid the visually impaired. Specifically, great efforthas been expended in the area of intraocular retinal prosthesis devicesin an effort to restore vision in cases where blindness is caused byphotoreceptor degenerative retinal diseases; such as retinitispigmentosa and age related macular degeneration which affect millions ofpeople worldwide.

Neural tissue can be artificially stimulated and activated by prostheticdevices that pass pulses of electrical current through electrodes onsuch a device. The passage of current causes changes in electricalpotentials across visual neuronal membranes, which can initiate visualneuron action potentials, which are the means of information transfer inthe nervous system.

Based on this mechanism, it is possible to input information into thenervous system by coding the sensory information as a sequence ofelectrical pulses which are relayed to the nervous system via theprosthetic device. In this way, it is possible to provide artificialsensations including vision.

One typical application of neural tissue stimulation is in therehabilitation of the blind. Some forms of blindness involve selectiveloss of the light sensitive transducers of the retina. Other retinalneurons remain viable, however, and may be activated in the mannerdescribed above by placement of a prosthetic electrode device on theinner (toward the vitreous) retinal surface (epiretinal). This placementmust be mechanically stable, minimize the distance between the deviceelectrodes and the visual neurons, control the electronic fielddistribution and avoid undue compression of the visual neurons.

In 1986, Bullara (U.S. Pat. No. 4,573,481) patented an electrodeassembly for surgical implantation on a nerve. The matrix was siliconewith embedded iridium electrodes. The assembly fit around a nerve tostimulate it.

Dawson and Radtke stimulated cat's retina by direct electricalstimulation of the retinal ganglion cell layer. These experimentersplaced nine and then fourteen electrodes upon the inner retinal layer(i.e., primarily the ganglion cell layer) of two cats. Their experimentssuggested that electrical stimulation of the retina with 30 to 100 μAcurrent resulted in visual cortical responses. These experiments werecarried out with needle-shaped electrodes that penetrated the surface ofthe retina (see also U.S. Pat. No. 4,628,933 to Michelson).

The Michelson '933 apparatus includes an array of photosensitive deviceson its surface that are connected to a plurality of electrodespositioned on the opposite surface of the device to stimulate theretina. These electrodes are disposed to form an array similar to a “bedof nails” having conductors which impinge directly on the retina tostimulate the retinal cells. U.S. Pat. No. 4,837,049 to Byers describesspike electrodes for neural stimulation. Each spike electrode piercesneural tissue for better electrical contact. U.S. Pat. No. 5,215,088 toNorman describes an array of spike electrodes for cortical stimulation.Each spike pierces cortical tissue for better electrical contact.

The art of implanting an intraocular prosthetic device to electricallystimulate the retina was advanced with the introduction of retinal tacksin retinal surgery. De Juan, et al. at Duke University Eye Centerinserted retinal tacks into retinas in an effort to reattach retinasthat had detached from the underlying choroid, which is the source ofblood supply for the outer retina and thus the photoreceptors. See,e.g., E. de Juan, et al., 99 Am. J. Ophthalmol. 272 (1985). Theseretinal tacks have proved to be biocompatible and remain embedded in theretina, and choroid/sclera, effectively pinning the retina against thechoroid and the posterior aspects of the globe. Retinal tacks are oneway to attach a retinal electrode array to the retina. U.S. Pat. No.5,109,844 to de Juan describes a flat electrode array placed against theretina for visual stimulation. U.S. Pat. No. 5,935,155 to Humayundescribes a retinal prosthesis for use with the flat retinal arraydescribed in de Juan.

US Patent Application 2003/0109903 to Peter G. Berrang describes a Lowprofile subcutaneous enclosure, in particular and metal over ceramichermetic package for implantation under the skin.

U.S. Pat. No. No. 6,718,209, US Patent Applications Nos. 2002/0095193and 2002/0139556 and US Patent Applications Nos. 2003/0233133 and2003/0233134 describe inter alia package for an implantable neuralstimulation device. Further descriptions of package for an implantableneural stimulation device can be found inter alia in U.S. Pat. No.7228181; and US Patent Applications Nos. 20050288733 and 20060247754,all of which are assigned to a common assignee and incorporated hereinby reference.

BRIEF SUMMARY OF THE INVENTION

The present invention is an improved hermetic package for implantationin the human body. The implantable device of the present inventionincludes an electrically non-conductive substrate including electricallyconductive vias through the substrate. A circuit is flip-chip bonded toa subset of the vias. A second circuit is wire bonded to another subsetof the vias. Finally, a cover is bonded to the substrate such that thecover, substrate and vias form a hermetic package.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the implanted portion of the preferredretinal prosthesis.

FIG. 2 is a side view of the implanted portion of the preferred retinalprosthesis showing the strap fan tail in more detail.

FIG. 3 is a perspective view of a partially built package showing thesubstrate, chip and the package wall.

FIG. 4 is a perspective view of the hybrid stack placed on top of thechip.

FIG. 5 is a perspective view of the partially built package showing thehybrid stack placed inside.

FIG. 6 is a perspective view of the lid to be welded to the top of thepackage.

FIG. 7 is a view of the completed package attached to an electrodearray.

FIG. 8 is a cross-section of the package.

FIG. 9 is a perspective view of the implanted portion of the preferredretinal prosthesis.

FIG. 10 is a cross-section of the three stack package.

FIG. 11 is a cross-section of the three stack package.

FIG. 12 is a cross-section of the two stack package.

FIG. 13 is a cross-section of the two stack package.

FIG. 14 is a cross-section of the two stack package.

FIG. 15 is a cross-section of the one stack package.

FIG. 16 is a cross-section of the folded stack package.

FIG. 17 is a cross-section of the package.

FIG. 18 is a cross-section of the package.

FIG. 19 is a cross-section of the lid shaping package.

FIG. 20 is a cross-section of the lid shaping package.

FIGS. 21 and 22 are cross-sections the package showing interconnects indetail.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims.

The present invention is an improved hermetic package for implantingelectronics within a body. Electronics are commonly implanted in thebody for neural stimulation and other purposes. The improved packageallows for miniaturization of the package which is particularly usefulin a retinal or other visual prosthesis for electrical stimulation ofthe retina.

FIG. 1 shows a perspective view of the implanted portion of thepreferred retinal prosthesis. A flexible circuit 1 includes a flexiblecircuit electrode array 10 which is mounted by a retinal tack (notshown) or similar means to the epiretinal surface. The flexible circuitelectrode array 10 is electrically coupled by a flexible circuit cable12, which pierces the sclera in the pars plana region, and iselectrically coupled to an electronics package 14, external to thesclera. Further an electrode array fan tail 15 is formed of moldedsilicone and attaches the electrode array cable 12 to a molded body 18to reduce possible damage from any stresses applied during implantation.

The electronics package 14 is electrically coupled to a secondaryinductive coil 16. Preferably the secondary inductive coil 16 is madefrom wound wire. Alternatively, the secondary inductive coil 16 may bemade from a flexible circuit polymer sandwich with wire traces depositedbetween layers of flexible circuit polymer. The electronics package 14and secondary inductive coil 16 are held together by the molded body 18.The molded body 18 holds the electronics package 14 and secondaryinductive coil 16 end to end. This is beneficial as it reduces theheight the entire device rises above the sclera. The design of theelectronic package (described below) along with a molded body 18 whichholds the secondary inductive coil 16 and electronics package 14 in theend to end orientation minimizes the thickness or height above thesclera of the entire device. This is important to minimize anyobstruction of natural eye movement.

The molded body 18 may also include suture tabs 20. The molded body 18narrows to form a strap 22 which surrounds the sclera and holds themolded body 18, secondary inductive coil 16, and electronics package 14in place. The molded body 18, suture tabs 20 and strap 22 are preferablyan integrated unit made of silicone elastomer. Silicone elastomer can beformed in a pre-curved shape to match the curvature of a typical sclera.However, silicone remains flexible enough to accommodate implantationand to adapt to variations in the curvature of an individual sclera. Thesecondary inductive coil 16 and molded body 18 are preferably ovalshaped. A strap 22 can better support an oval shaped secondary inductivecoil 16.

Further it is advantageous to provide a sleeve or coating 50 thatpromotes healing of the sclerotomy. Polymers such as polyimide, whichmay be used to form the flexible circuit cable 12 and flexible circuitelectrode array 10, are generally very smooth and do not promote a goodbond between the flexible circuit cable 12 and scleral tissue. A sleeveor coating of polyester, collagen, silicone, Gore-tex or similarmaterial would bond with scleral tissue and promote healing. Inparticular, a porous material will allow scleral tissue to grow into thepores promoting a good bond.

It should be noted that the entire implant is attached to and supportedby the sclera. An eye moves constantly. The eye moves to scan a sceneand also has a jitter motion to improve acuity. Even though such motionis useless in the blind, it often continues long after a person has losttheir sight. By placing the device under the rectus muscles with theelectronics package in an area of fatty tissue between the rectusmuscles, eye motion does not cause any flexing which might fatigue, andeventually damage, the device.

FIG. 2 shows side view of the implanted portion of the retinalprosthesis, in particular, emphasizing the strap fan tail 24. Whenimplanting the retinal prosthesis, it is necessary to pass the strap 22under the eye muscles to surround the sclera. The secondary inductivecoil 16 and molded body 18 must also follow the strap 22 under thelateral rectus muscle on the side of the sclera. The implanted portionof the retinal prosthesis is very delicate. It is easy to tear themolded body 18 or break wires in the secondary inductive coil 16 orelectrode array cable 12. In order to allow the molded body 18 to slidesmoothly under the lateral rectus muscle, the molded body 18 is shapedin the form of a strap fan tail 24 on the end opposite the electronicspackage 14.

FIG. 3 shows the hermetic electronics package 14 is composed of aceramic substrate 60 brazed to a metal case wall 62 which is enclosed bya laser welded metal lid 84. The metal of the wall 62 and metal lid 84may be any biocompatible metal such as Titanium, niobium, platinum,iridium, palladium or combinations of such metals. The ceramic substrateis preferably alumina but may include other ceramics such as zirconia.The ceramic substrate 60 includes vias (not shown) made frombiocompatible metal and a ceramic binder using thick-film techniques.The biocompatible metal and ceramic binder is preferably platinum flakesin a ceramic paste or frit which is the ceramic used to make thesubstrate. After the vias have been filled, the substrate 60 is firedand lapped to thickness. The firing process causes the ceramic tovitrify biding the ceramic of the substrate with the ceramic of thepaste forming a hermetic bond. Thin-film metallization 66 is applied toboth the inside and outside surfaces of the ceramic substrate 60 and anASIC (Application Specific Integrated Circuit) integrated circuit chip64 is bonded to the thin film metallization on the inside of the ceramicsubstrate 60.

The inside thin film metallization 66 includes a gold layer to allowelectrical connection using wire bonding. The inside film metallizationincludes preferably two to three layers with a preferred gold top layer.The next layer to the ceramic is a titanium or tantalum or mixture oralloy thereof. The next layer is preferably palladium or platinum layeror an alloy thereof. All these metals are biocompatible. The preferredmetallization includes a titanium, palladium and gold layer. Gold is apreferred top layer because it is corrosion resistant and can be coldbonded with gold wire.

The outside thin film metallization includes a titanium adhesion layerand a platinum layer for connection to platinum electrode array traces.Platinum can be substituted by palladium or palladium/platinum alloy. Ifgold-gold wire bonding is desired a gold top layer is applied.

The package wall 62 is brazed to the ceramic substrate 60 in a vacuumfurnace using a biocompatible braze material in the braze joint.Preferably, the braze material is a nickel titanium alloy. The brazetemperature is approximately 1000° Celsius. Therefore the vias and thinfilm metallization 66 must be selected to withstand this temperature.Also, the electronics must be installed after brazing. The chip 64 isinstalled inside the package using thermocompression flip-chiptechnology. The chip is underfilled with epoxy to avoid connectionfailures due to thermal mismatch or vibration.

FIGS. 4 and 5 show off-chip electrical components 70, which may includecapacitors, diodes, resistors or inductors (passives), are installed ona stack substrate 72 attached to the back of the chip 64, andconnections between the stack substrate 72 and ceramic substrate 60 aremade using gold wire bonds 82. The stack substrate 72 is attached to thechip 64 with non-conductive epoxy, and the passives 70 are attached tothe stack substrate 72 with conductive epoxy.

FIG. 6 shows the electronics package 14 is enclosed by a metal lid 84that, after a vacuum bake-out to remove volatiles and moisture, isattached using laser welding. A getter (moisture absorbent material) maybe added after vacuum bake-out and before laser welding of the metal lid84. The metal lid 84 further has a metal lip 86 to protect componentsfrom the welding process and further insure a good hermetic seal. Theentire package is hermetically encased. Hermeticity of the vias, braze,and the entire package is verified throughout the manufacturing process.The cylindrical package was designed to have a low profile to minimizeits impact on the eye when implanted.

The implant secondary inductive coil 16, which provides a means ofestablishing the inductive link between the external video processor(not shown) and the implanted device, preferably consists of gold wire.The wire is insulated with a layer of silicone. The secondary inductivecoil 16 is oval shaped. The conductive wires are wound in definedpitches and curvature shape to satisfy both the electrical functionalrequirements and the surgical constraints. The secondary inductive coil16, together with the tuning capacitors in the chip 64, forms a parallelresonant tank that is tuned at the carrier frequency to receive bothpower and data.

FIG. 7 shows the flexible circuit 1, includes platinum conductors 94insulated from each other and the external environment by abiocompatible dielectric polymer 96, preferably polyimide. One end ofthe array contains exposed electrode sites that are placed in closeproximity to the retinal surface 10. The other end contains bond pads 92that permit electrical connection to the electronics package 14. Theelectronic package 14 is attached to the flexible circuit 1 using aflip-chip bumping process, and epoxy underfilled. In the flip-chipbumping process, bumps containing conductive adhesive placed on bondpads 92 and bumps containing conductive adhesive placed on theelectronic package 14 are aligned and melted to build a conductiveconnection between the bond pads 92 and the electronic package 14. Leads76 for the secondary inductive coil 16 are attached to gold pads 78 onthe ceramic substrate 60 using thermal compression bonding, and are thencovered in epoxy. The electrode array cable 12 is laser welded to theassembly junction and underfilled with epoxy. The junction of thesecondary inductive coil 16, array 1, and electronic package 14 areencapsulated with a silicone overmold 90 that connects them togethermechanically. When assembled, the hermetic electronics package 14 sitsabout 3 mm away from the end of the secondary inductive coil.

Since the implant device is implanted just under the conjunctiva it ispossible to irritate or even erode through the conjunctiva. Erodingthrough the conjunctiva leaves the body open to infection. We can doseveral things to lessen the likelihood of conjunctiva irritation orerosion. First, it is important to keep the over all thickness of theimplant to a minimum. Even though it is advantageous to mount both theelectronics package 14 and the secondary inductive coil 16 on thelateral side of the sclera, the electronics package 14 is mounted higherthan, but not covering, the secondary inductive coil 16. In other wordsthe thickness of the secondary inductive coil 16 and electronics packageshould not be cumulative.

It is also advantageous to place protective material between the implantdevice and the conjunctiva. This is particularly important at thescleratomy, where the thin film electrode array cable 12 penetrates thesclera. The thin film electrode array cable 12 must penetrate the sclerathrough the pars plana, not the retina. The scleratomy is, therefore,the point where the device comes closest to the conjunctiva. Theprotective material can be provided as a flap attached to the implantdevice or a separate piece placed by the surgeon at the time ofimplantation. Further material over the scleratomy will promote healingand sealing of the scleratomy. Suitable materials include Dacron, Teflon(polytetraflouroethylene or PTFE), Goretex (ePTFE) Tutoplast (sterilizedsclera), Mersilene (Polyester) or silicone.

FIG. 8 shows the package 14 containing a ceramic substrate 60, withmetallized vias 65 and thin-film metallization 66. The package 14contains a metal case wall 62 which is connected to the ceramicsubstrate 60 by braze joint 61. On the ceramic substrate 60 an underfill69 is applied. On the underfill 69 an integrated circuit chip 64 ispositioned. On the integrated circuit chip 64 a ceramic hybrid substrate68 is positioned. On the ceramic hybrid substrate 68 passives 70 areplaced. Wirebonds 67 are leading from the ceramic substrate 60 to theceramic hybrid substrate 68. A metal lid 84 is connected to the metalcase wall 62 by laser welded joint 63 whereby the package 14 is sealed.

FIG. 9 shows a perspective view of the implanted portion of thepreferred retinal prosthesis which is an alternative to the retinalprosthesis shown in FIG. 1.

The electronics package 14 is electrically coupled to a secondaryinductive coil 16. Preferably the secondary inductive coil 16 is madefrom wound wire. Alternatively, the secondary inductive coil 16 may bemade from a flexible circuit polymer sandwich with wire traces depositedbetween layers of flexible circuit polymer. The electronics package 14and secondary inductive coil 16 are held together by the molded body 18.The molded body 18 holds the electronics package 14 and secondaryinductive coil 16 end to end. The secondary inductive coil 16 is placedaround the electronics package 14 in the molded body 18. The molded body18 holds the secondary inductive coil 16 and electronics package 14 inthe end to end orientation and minimizes the thickness or height abovethe sclera of the entire device.

Lid 84 and case wall 62 may also contain titanium or titanium alloy orother metals and metal alloys including platinum, palladium, gold,silver, ruthenium, or ruthenium oxide. Lid 84 and case wall 62 may alsocontain a polymer, copolymer or block copolymer or polymer mixtures orpolymer multilayer containing parylene, polyimide, silicone, epoxy, orPEEK™ polymer. Via substrate may be preferably contain alumina orzirconia with platinum vias.

FIG. 15 shows one stack assembly. One stack means that all of the partsare on a chip, with our without a separate demux. A via substrate isplaced on the bottom below a flip IC which includes RF Transceiver,power recovery, drivers, and an optional demux.

FIGS. 12, FIG. 13 and FIG. 14 show two stack assemblies. FIG. 16 shows afolded stack assembly. FIG. 12 shows a ceramic substrate next to RFtransceiver/power recovery chip and both placed on a flipchipdriver/demux. FIG. 13 shows ceramic substrate on a flipchipdriver/demux. RF transceiver/power recovery chip is provided on theceramic substrate. FIG. 14 shows ceramic substrate on to of a flipchipdriver/demux. RF transceiver/power recovery chip is provided notdirectly on the ceramic substrate. The difference between FIG. 13 andFIG. 14 is that in FIG. 13 the ceramic substrate is in direct contactwith RF transceiver/power recovery chip but not in FIG. 14. Thesubstrate can be ceramic but also any kind of polymer or glass. FIG. 16shows a folded stack substrate and a flipchip demux on the bottom and anIC placed on the flip chip demux. The substrate is folded twice.

FIG. 10 and FIG. 11 show a three stack assembly. A three stack demuxflip-chip bonded to substrate with chip and hybrid wire-bonded above ispreferred. FIG. 10 shows a ceramic substrate on a IC including a RFtransceiver/power recovery drivers and the IC is placed on a flipchipdriver/demux. FIG. 11 shows a similar assembly as FIG. 10 however theceramic substrate is placed on pedestal which is placed between thesubstrate and the IC.

FIG. 17 and FIG. 18 show additional flip chip configurations. Bothfigures have a similar assembly. However, in FIG. 17 the IC is bonded toflipchip demux by a bump bond. In FIG. 18 a double sided multilayerceramic substrate is bonded to the IC by a bump bond.

They can be two stack or folded stack and could be one or two-sided. Itmay be passive on the substrate next to IC. A pedestal is useful butoptional to make room for wire bonds. A through via means that via goesthrough the IC. A bump bond to IC and then bump bond to IC to passivesubstrate or demux is possible. Bond pads on IC to line up with vias toeliminate the inside metallization can be provided. Driver IC flipchipcan be bonded to substrate with passives. Demux flip-chip can be bondedto via substrate and the two substrates can be wire-bonded or flexcircuit bonded together. Driver portion can be moved to demux chip andeverything else to a separate chip to reduce interconnect lines. Twostack chip can be provided with smaller chip (RF and demux) and hybridabove. It may include wire-bonds directly from the Hybrid to the chip.Chip may include a demux driver on the same wafer.

FIG. 19 and FIG. 20 show different variations of the lid shape. Possibleis a concave lid to conform to eye.

FIG. 21 and FIG. 22 are cross-sections the package showing interconnectsin detail. Both figures show redistribution routings and interconnect onthe top and the bottom of via substrate. Redistribution routing on topof the via substrate and the braze stop on top of the via substratecontain preferably metals like Ti, Zr, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt,Cu, Ag, Au, mixtures, layers or alloys thereof. The top layer of the topredistribution routing is gold or gold alloy. Redistribution routing onbottom of the via substrate and the braze stop on top of the viasubstrate contain preferably metals like Ti, Zr, Fe, Ru, Co, Rh, Ir, Ni,Pd, Pt, Cu, Ag, Au, mixtures, layers or alloys thereof. The top layer ofthe top redistribution routing is platinum or platinum alloy.Interconnect and redistribution routing is the connection the bondbetween flexible circuit and via substrate on the bottom of thesubstrate and a connection between the chip and the substrate on top ofthe substrate. The walls in FIG. 22 show the same braze metal asmentioned before as a flange.

Accordingly, what has been shown is an improved method making a hermeticpackage for implantation in a body. While the invention has beendescribed by means of specific embodiments and applications thereof, itis understood that numerous modifications and variations could be madethereto by those skilled in the art without departing from the spiritand scope of the invention. It is therefore to be understood that withinthe scope of the claims, the invention may be practiced otherwise thanas specifically described herein.

What we claim is:
 1. An implantable device, comprising: A firstelectrically non-conductive substrate; a plurality of electricallyconductive vias through the first electrically non-conductive substrate;conductive traces deposited on the first electrically non-conductivesubstrate, the first electrically non-conductive substrate, electricallyconductive vias and conductive traces forming a base; a flip-chipcircuit attached to the base using conductive bumps; a stack chipcircuit bonded to the flip chip circuit and wire bonded to the base; asecond electrically non-conductive substrate bonded to the stack chipcircuit and wire bonded to the base; discrete passives attached to thesecond electrically non-conductive substrate; and a cover bonded to thebase, the cover and the base forming a hermetic package.
 2. Theimplantable device according to claim 1, wherein the electricallyconductive vias are a metallic and ceramic paste co-fired with the firstelectrically non-conductive substrate to form a hermetic seal.
 3. Theimplantable device according to claim 1, wherein the cover is brazed tothe base.
 4. The implantable device according to claim 3, furthercomprising a braze stop on said first electrical nonconductive substrateand along a periphery of said electrically non-conductive substratesurrounding the plurality of electrically conductive vias and separatinga braze joint from said plurality of electrically conductive vias. 5.The implantable device according to claim 1, wherein the conductivetraces are metal traces.
 6. The implantable device according to claim 5,wherein the metal traces are chosen to withstand braze temperatures. 7.The implantable device according to claim 5, wherein the metal tracescomprise one or more of the metals titanium, tantalum, gold, palladium,platinum or layers or alloys thereof.
 8. The implantable deviceaccording to claim 1, further comprising a flexible circuit bump bondedto the vias.
 9. The implantable device according to claim 1, furthercomprising metal traces deposited on the first electricallynon-conductive substrate and in contact with the electrically conductivevias; and a flexible circuit attached to the metal traces.
 10. Theimplantable device according to claim 8, wherein the flexible circuit isan electrode array suitable for stimulating tissue.
 11. The implantabledevice according to claim 1, further comprising a polymer underfillunder the flip-chip circuit.
 12. The implantable device according toclaim 1, wherein the conductive bumps contain at least one conductivepolymer.
 13. The implantable device according to claim 1, wherein theconductive bumps contain at least one conductive epoxy or polyimide. 14.The implantable device according to claim 1, wherein the conductivebumps are filled with one or more metals selected from the groupcomprising silver, platinum, iridium, titanium, platinum alloys, iridiumalloys, or titanium alloys or mixtures thereof.
 15. The implantabledevice according to claim 14, wherein the metal or metal alloys are indust, flake, or powder form.